Jaw function has been studied as a function of tooth contacts. Less attention has been directed to jaw function out of dental occlusion. This study is the development and application of a method of quantitatively assessing mandibular motion. It uses light-emitting diodes attached to clutches attached to patients' teeth. Light emitted from the diodes is recorded on film using a high-speed camera. The film is developed and digitized to magnetic tape using automated equipment. The magnetic tape is entered for computer quantitation and analysis. The object of this study is the quantitation of jaw function. The above described system will be used for three broad groups of patients. Group 1 will be patients experiencing various forms of orthognathic surgery. This will allow acute form and function analysis. Group 2 will be patients representing extreme variations in growth and development which will allow developmental change analysis. Group 3 will be patients with temporomandibular joint symptoms. All groups will be studied at intervals to permit analysis, consistency of pattern, and effects of treatment on function.